Ultegra RX vs. GRX 812 for 1x drivetrain

Just converted my 2x gravel bike to 1x for some winter CX mud.

Still using my Ultegra RX mech but have fitted an 11-40 cassette.

The shifting ‘works’ but it isn’t great, and especially when you’re churning around in the mud barely in control it’s frustrating not being *absolutely* sure it’s in gear when you shift.

Thing is though, this has been my experience of 1x drivetrains in general, I never really got my old SRAM GX 1×11 working perfectly either, compared to 2x drivetrains with smaller cassettes.

Would a 1x specific mech improve shifting noticeably? I’m assuming they can track the bigger cassette better unlike the Ultegra RX mech which only works with the B-tension screwed all the way in.

£85 quid experiment, just hoping somebody else has gone from a bodged set-up to a ‘proper’ set up and can convince me it’s worth it….

Ta

Don’t suppose it’d help for me to say my ultegra rx works fine 1×11 ? (only 11-28 I think)

Can’t help yet…but…Just ordered grx812, grx 1x shifters and 11-46 slx cassette (bigger than shimano approve but apparently works fine)…will report back on shifting quality once fitted.

It may not be relevant but I love how my left hand GRX sti works the dropper 😁

11-40 does seem pretty huge for ultegra though

GRX 812 mech with 600 shifters here with an 11-42 SunRace cassette. Shifting is great, feels much smoother that the Rival that was on before and once settled in it runs as quiet across the range as the Ultegra 34/50 11-28 on my other bike.

11-40 does seem pretty huge for ultegra though

I’m running an Ultegra rear mech on a 11-40T cassette and  50/34 up front. It’s spot-on.

Don’t suppose it’d help for me to say my ultegra rx works fine 1×11 ? (only 11-28 I think)

Yeah, the Ultegra RX worked perfectly on an 11-34 cassette in my 2x setup, which funnily enough is the maximum range Shimano recommend. I knew it would run 11-40, just wasn’t sure if sluggish shifting in certain gears was to be expected.

Will give it another couple of tweaks but think I’ll just be trading one uncertain change for another depending on cable tension.

Shifting is great, feels much smoother that the Rival that was on before

Cheers. ‘Smoother than SRAM’ isn’t saying much based on my experience but at least the shifting is good!

GRX all day every day, just for the lever shape

Running 40×11-51 with 812 levers & mech

GRX all day every day, just for the lever shape

I always say my bike has a GRX drivetrain but in reality it’s 105 shifters (with a 1x TRP brake lever on the LHS now) with GRX cranks, XT cassette and Ultegra rear mech. So 4 different groupsets and 2 different manufacturers. Is a miracle it works at all 😀

The Ultegra RX mech has a maximum recommended large sprocket size of 34T so you really need to fit something like a goat link hanger extender to give enough clearance between the jockey wheel and big sprocket to make it work, or get the GRX mech…

The Ultegra RX mech has a maximum recommended large sprocket size of 34T so you really need to fit something like a goat link hanger extender to give enough clearance between the jockey wheel and big sprocket to make it work, or get the GRX mech…

Yeah, that’s the crux of it, I can get the Ultegra RX to accommodate the 40 tooth cassette without a goat link, and for the most part it shifts OK, just seems to hang up on a couple of gears. I’m just trying to figure out if the GRX would be £85 better! I guess the first time I try to thrash my way up a muddy slope and the gear slips I’ll be wishing I’d spent the money…

The Ultegra RX mech has a maximum recommended large sprocket size of 34T so you really need to fit something like a goat link hanger extender to give enough clearance between the jockey wheel and big sprocket to make it work,

Many folk (including me) have it working just fine without a hanger extender.

Running Ultegra RX here with 11-42 cassette and no extra hanger thing it works like a charm, it maybe dropout geometry dependent I guess?

Hmm, rats, if you can get Ultegra RX working smoothly then makes me wonder if the mech is the issue after all!

Best check hanger alignment again, feels like I’ve only just straightened it but the bike does to end up on its side quite often!

RX mech and 40t here, works perfectly.

Yep probably not the mech to be fair…

Hmm, fairly graphic demonstration that it WAS the mech struggling with the 11-40 cassette, after half an hour of frustration I just stuck an 11-34 cassette back on and the shifting was sweet as a nut!

Guess I’ll be forking out for that GRX 812 derailleur then! 😂

I’ve just gone from 2x Ultegra R8000 (50/34 and 11-34) to 1 x GRX812 mech and 40t chainset with 11-42 XT cassette, shifts well. Offset nearly all cost by flogging ultegra stuff on ebay.

On a side note, how crappy are Shimano’s new barrel adjusters?

It seems to be a very soft plastic collar trying to turn a very stiff metal barrel!

Have ordered a spare 105 5800 adjuster to replace the existing one, and some inline adjusters for the bike so I don’t need to even touch the new one…

I went from an Ultegra RX to a GRX812 and so much better shifting. Sorry.

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Purists and brand evangelists look away now. #sramforce 12 speed chain, #sramxg1150 11 speed cassette, #shimanogrx812 derailleur and classic #duraace7900 10 speed crank and narrow-wide chainring. Because #gravgrav #diyfs

A post shared by Thom (@thomthebike) on Feb 7, 2020 at 8:36am PST

I’ve repeatedly struggled to get my RX shifting well too on 1 x 11. Not so much in the dry but in a muddy race it’s crap. Next season I might go back to 2×10 tiagra like my pit/turbo/commuter because that consistently works like a dream!

I went from an Ultegra RX to a GRX812 and so much better shifting. Sorry.

It’s ok, I’ve ordered the new mech, so now you’re telling me what I want to hear instead 🙂

I’m kicking myself because I had planned to experiment with the Ultegra mech on the 11-40 cassette BEFORE spending money on other drivetrain bits.

Instead I spent £80 on a lovely looking Garbaruk chainring which kind of commits me to the 11-40 cassette as the gearing would be too high otherwise.

If I hadn’t ordered the bigger chainring I could probably have used my old 11-34 cassette with my existing 36 tooth ring. D’oh!

Ah well, can at least hold on to the Ultegra/11-34 setup for our trip to the Pyrenees next year, I suspect after a few of those climbs I’ll be glad of the bailout gears!

If it makes you feel even better then I experimented with various chainrings and rear derailleurs and links before buying the RX then finding it didn’t work so well then buying the GRX.
And I’m still not sure of I should just go 2x with a mtb crack and have much better gear ratio spread.
For reference I have 37t single ring with 10-42 cassette and the grx derailleur.
If I went to the mtb crank I could go 25/40t up front and 11-32 cassette with a smaller and lighter rear derailleur. I already have a Red front derailleur so not very heavy. I haven’t looked at ratios in terms of numbers yet. Nor have I weighed components.

I think there are some weight savings, I dropped almost 1kg going from my summer long distance/gravel build to my winter 1x CX build. About 300g of that was tyres, 100g was 1 layer of handlebar tape, 250g was the suspension seatpost. So probably saved about 300g going 1x (and I even went to the trouble of replacing the 2x 105 front shifter with a 1x TRP brake lever).

I mainly did it though for the mud-proofing, even if no CX racing happens this year I wanted to test out the 1x setup and have a play on some local muddy stuff. If it works well enough I might not go back, can just switch chainrings if I want to do any more hilly credit card touring next summer.

I did some ratio calculations and based upon the above 2x v 1x gear solutions I’d gain a lower ratio climbing gear but my top end would be so close to not be worth debating. Comes down to weight then. Of course I could skew the comparison as I have a power2max crankset as 1x which is much heavier than the Rotor 3d+ Crank I’d use for 2x but that’s not really fair. I imagine most of the weight saved would be in the cassette swap, but would that be mitigated by the inclusion of a front derailleur and cable? The wheels are the heaviest items at 2kg for the pair; mostly down to the Son dynamo hub and 32 spokes laced to xm421 rims. But I’m not swapping those until summer.

In case anyone interested. Grx 812 with 11-46 and a 42 chainring, and shifting seems sweet. New chain only just long enough though!

I’ve had a few mongrel gear setups on my bikes and think they’re fine only to ride a bike with a full groupset of matching components then realising just how much better they work in comparison.

Still happy with my full GRX 1x setup as I love 1x off road as I’ve one less thing to concern myself with, despite occasionally finding myself wanting a slightly bigger gear on the road and a slightly smaller gear when off road. I don’t race though.

Installed the new mech, immediately a massive improvement over trying to make the Ultegra RX mech work.

Unfortunately the first ride was a super muddy/grassy/leafy CX affair so things rapidly got clogged!

The shifting off the lowest gear/largest sprocket is still quite slow, might be a B-Tension thing but I noticed this on my SRAM setup as well, more fiddling required!

Just following up rather than starting a new thread, now that I have all the ‘correct’ components, why is the shifting off the lowest gear/largest sprocket still lousy?

Chain length is fine, possibly half a link too long. Cable tension is fine (i.e. if I slacken it enough to improve the shifting off the biggest cog, I then can’t shift back up the block). If it is B-tension then there seems to be a very fine margin between too much and too little, Shimano don’t seem to specify and exact distance like SRAM (god help me, I’m praising SRAM…).